1. Field of the Disclosure
The described technology relates to a fuel cell stack. More particularly, it relates to a structure of a separator of a fuel cell stack.
2. Description of the Related Technology
A fuel cell system includes a fuel cell stack that generates electrical energy using electrochemical reaction of a fuel (hydrocarbon-based fuel, pure hydrogen, or reformed gas rich in hydrogen) and an oxidizing agent (air or pure oxygen). The fuel cell stack includes a plurality of membrane-electrode assemblies (MEAs) and a plurality of separators formed between the MEAs.
A MEA includes an electrolyte membrane, an anode formed at one side of the electrolyte membrane, and a cathode formed at the other side of the electrolyte membrane. The separator on the anode side of the MEA is formed with a fuel channel on the surface facing the anode. The separator on the cathode side of the MEA is formed with an oxidant channel on the surface facing the cathode. Two fuel manifolds and two oxidant manifolds are formed on an edge of each separator. The fuel channel is in fluid communication with two fuel manifolds, and the oxidant channel is in fluid communication with two oxidant manifolds.
In operation, fuel supplied through a first fuel manifold passes through the fuel channel and is provided to the anode. Unreacted fuel is exhausted through a second fuel manifold. Similarly, oxidant supplied through a first oxidant manifold passes through the oxidant channel and is provided to the cathode. Moisture and unreacted air is exhausted through a second oxidant manifold of the opposite side. The oxidant channel and the fuel channel are formed of a concave groove having a small width and a long length, thereby having a smaller cross-section than the oxidant manifold and the fuel manifold. Accordingly, the pressure of the fluid quickly increases both when the oxidant enters the oxidant channel from the oxidant manifold and the fuel enters the fuel channel from the fuel manifold. As a result, high pressure of the fluid is concentrated in the region where the fuel initially enters among the anode and the oxidant initially enters among the cathode. This high pressure makes it is difficult to uniformly distribute the fuel and the oxidant at the entrances of the fuel channel and the oxidant channel, respectively.
Further, because the oxidant supplied to the fuel cell stack is in a non-humidified state, the region where the oxidant is initially supplied to the cathode operates in a very dry state. This dry state may increase radicals generated during operation of the membrane-electrode assembly, which consequently may hasten deterioration of the membrane-electrode assembly.